Interestingly, what the King says reflects the contemporary concept of "Litthauen" and "Litthauer" of the 19th century, which included ethnic Germans. You could be German and Lithuanian at the same time !
In order to distinguish the ethnic Lithuanian from the ethnic German the King adds "eigentlich" meaning "proper".

The sentence also shows that the ethnic Lithuanians of Prussia were regarded as autochthons:
"eingeboren" means "native".